Refrigerating system including a hot gas defrosting circuit



July 21, 1959 NQNQMAQUE 2,895,307

REFRIGERATING SYSTEM INCLUDING A HOT GAS DEFROSTING CIRCUIT Filed Dec. 20, 1957 I GDDUUUDUU EDD CID INVENTOR. i CLYDE vJ. NONOMAQU;

Hi5 ATTORNEY United States l atent REFRIGERATIN G SYSTEM INCLUDING A HOT GAS DEFROSTING CIRCUIT Clyde J. Nonomaque, Louisville, Ky., assignor to General Electric Company, a corporation of New York Application December 20, 1957, Serial No. 704,129

2 Claims. (Cl. 62- 156) The present invention relates to refrigerating apparatus and is more particularly concerned with a refrigerating system including an improved circuit arrangement for employing compressed refrigerant gas for defrosting the evaporator component of the system.

In my copending application SN. 698,462 filed November 25, 1957 and assigned to the same assignee as the present invention, there is described and claimed a refrigerating system including an auxiliary hot gas defrosting circuit for quickly and effectively defrosting the evaporator component of the refrigerant system by means of compressed refrigerant.

The refrigerant system described in my copending application preferably comprises a hermetic compressor, a condenser, a fixed fiow restrictor and an evaporator connected to form a series-flow normal refrigerating circuit in which the refrigerant passing throughthe hermetic casing cools the motor employed for driving the compressor. For the purpose of periodically raising the evaporator to defrost temperatures by means of hot compressed refrigerant from the compressor, there is provided an auxiliary circuit connected between the high and low pressure sides of the normal refrigerating circuit and in parallel with at least that part of the normal circuit including the fixed flow restrictor and the evaporator. This auxiliary circuit includes a defrost portion in heat exchange with the evaporator and a flow restricting means between the defrost portion and the compressor so that upon opening of a normally closed valve in the auxiliary circuit, hot compressed refrigerant will flow through the defrost portion of the auxiliary circuit'in heating relation with the evaporator where condensation of refrigerant in the defrosting portion quickly and effectively warms the evaporator to defrosting tempenatures. The refrigerant condensed in the defrost portion then .passes through the flow restricting means in the auxiliary circuit and back to the compressor case Where it produces refrigeration and increases the load on the refrigerant cooled compressor motor, causing the input waits to the r'notor' to increase and thereby providing additional energy in ;the form of heat for defrosting operations.

During operation of the refrigerating system described ,in my aforementioned application: both the auxiliary circuit and the normal refrigerating circuit are open to the compressor. As is pointed out in the application, this is a particularly advantageous feature in that, while a large amount of heat is provided by the heavily loaded compressor motor during the defrost operation, it is unnecessary to provide the system with any over temperature protection. With both circuits open to the compressor during the defrost operation, if pressures become excessive, condensation of the refrigerant will take place in the normal circuit condenser and the refrigeration resulting from flow through the normal circuit will counteractthe heating action of the auxiliary circuit thereby preventingfurther pressure rises.

I Ioweve r, under certain relatively low ambient tem- Patented July 21, 1959 perature conditions and for some applications of refrigerating systems where an extremely fast defrost operation is required, it may be desirable to prevent all flow through the normal refrigerating circuit during defrost operation. In addition to providing a valve in the normal refrigerating circuit for closing this circuit during defrost operation, the present invention has as an object the provision of an improved control circuit for controlling both the operation of the normally closed valve in the auxiliary circuit and the added valve in such a manner that the operation of the added valve is delayed a period of time after closing of the auxiliary circuit valve suflicient to permit any refrigerant present in the condenser to be transferred to the auxiliary or defrost circuit be fore closing of that valve whereby this refrigerant is available during defrost for increasing the load on the compressor.

Therefore in accordance with the present invention the refrigerating system of my aforementioned application is modified by the provision of a second, normally open valve in the normal refrigerating circuit between the compressor and the condenser and the provision of an electrical control circuit comprising both means for opening the first valve to initiate flow or refrigerant from the compressor through the defrost circuit and means responsive to a change in a system condition following opening of the first valve for closing the second or added valve, thereby preventing further flow of refrigerant through the normal refrigerating circuit until such time as the defrost operation is terminated.

For a better understanding of the present invention, reference may be had to the accompanying drawing in which the single figure is a diagrammatic illustration of a refrigerating apparatus embodying the hot gas defrost system of the present invention.

With reference to the drawing there is illustrated a preferred embodiment of the present invention comprising the usual components of a refrigerating system including a hermetic motor-compressor unit 1, a condenser 2, a fixed flow restrictor 3, preferably of the capillary tube type, a cooling or evaporator unit or structure 4 and a suction line 5 connected in series-flo-w relationship. Preferably, in accordance with the usual practice, the suction line 5 is in heat exchange with a portion of the flow restrictor 3 as indicated at 8. The evaporator structure 4, including an evaporator circuit 6 and, in the illustrated modification, an accumulator 7 may, and as is shown does, form part of a roll-bond or rollforged evaporator structure which includes the plate or body portion 9; the accumulator 7 in such case conveniently be composed of a plurality of intersecting vertical and horizontal tubular portions in accordance with the known practices.

The motor compressor unit 1 comprises a motor 14} for driving a compressor 11, the two being sealed in hermetic casing 12. A body of oil 14 is provided in the lower portion of the casing 12 and is circulated Within the casing by means of an oil pump (not shown) for lubricating the compressor and motor. The suction line 5 is connected to the case 12 so that the case is part of the low pressure side of the normal system and is therefore filled with low pressure refrigerant in cooling contact with the motor 10 while the compressor 11, having its inlet 15 communicating with the interior of the case 12, discharges the high pressure refrigerant directly through the discharge line 16 to the condenser 2. In this refrigerating circuit, the evaporator unit components 6, 7 and the case 15 form the low pressure side of the normal refrigerating circuit while the compressor 11 and the condenser 2 comprise the high pressure side.

. In a typical application of a refrigeration system of this type, the evaporator structure is placed in a cabinet (not shown) which is to be cooled, while the condenser 3 is placed in the ambient atmosphere. During the normal operation of the refrigerating system thus far described, the refrigerant fiow path is that indicated by the solid arrows. The motor-compressor unit 1 withdraws vaporized refrigerant from the top of the accumulator 7 through the suction line and discharges compressed refrigerant in a gaseous state to the condenser 2 where it is liquified. The refrigerant liquified in the condenser 2 passes through the capillary flow restrictor 3 into the evaporator circuit 6, where at a lower pressure, it vaporizes by absorbing heat from the refrigerator cabinet thus cooling the contents of the cabinet. Any liquid refrigerant not evaporated in the evaporator circuit 6 collects in the accumulator 7; the connection of the evaporator circuit 6 to the accumulator preferably being at the lower part of the accumulator while the suction line 5 is connected to the upper portion thereof so that during normal refrigerating operation of the system, only gaseous refrigerant is withdrawn from the accumulator through the suction line 5 by the motor compressor unit 1. Since the line 5 is in heat exchange at 8 with the restrictor 3, condensed refrigerant passing to the evaporator is further cooled by the refrigerant gas returning through the suction line.

To accomplish the defrosting of the evaporator structure 4, there is provided an auxiliary circuit 18 which is connected to the normal refrigerating circuit in parallel relationship with the evaporator component 6, 7 and restrictor 3 of the normal circuit in such a manner that, along with the remaining elements of the normal refrigerating circuit, the auxiliary circuit forms a defrost circuit for the circulation of compressed refrigerant gas from the compressor into heat exchange relationship with the evaporator structure 4 so as to warm this structure to defrosting temperatures. The inlet end 19 of the auxiliary circuit is connected to the discharge line 16 leading from the compressor to the condenser -2 and a normally closed valve 20 is provided for preventing flow of refrigerant through the auxiliary circuit 18 during normal refrigerating operation of the system. The auxiliary circuit also includes an evaporator defrosting portion composed of one section 22 in heat exchange relationship with accumulator 7 and a second section 23 running substantially parallel to the various passes of the serpentine evaporator circuit 6 and in heat exchange relationship therewith. The outlet end of the auxiliary circuit is connected to the suction line 5 as indicated by the numeral 24 through a restrictor tube 25 which provides sufiicient restriction to flow of refrigerant through the auxiliary circuit during defrost operation to maintain the compressed refrigerant gas in the defrost sections 22 and 23 at condensing pressures.

In the illustrated embodiment of the invention, the defrosting portion of the auxiliary circuit 18 comprising the section 22 and the section 23 also conveniently forms an integral part of the evaporator structure 4 when that structure is formed for example by the roll-bond process. Alternatively, it may comprise a separate tubular element brazed or otherwise secured to the evaporator structure 4. Also, the auxiliary circuit and the evaporator circuit may be in the form of a double-tube extrusion in which one tube is the evaporator conduit and'the other the defrost conduit.

In accordance with the present invention and for the purpose of preventing any flow of refrigerant through the normal refrigerating circuit during defrost operation, there is also provided a normally opened valve 27 in the normal refrigerating circuit between the auxiliary circuit inlet 19 and the condenser 2. When defrosting of the evaporator structure is required, thevalve 20 is first opened with the result that, due to the pressure diiferential and temperature conditionsvresulting upon opening of this valve, refrigerant stored in the condenser 2 re verse flows through the open valve 27 and into the auxiliary circuit 18. Thereafter and in response to a change in a system condition following opening of valve 20, valve 27 is closed to prevent any flow of refrigerant through the normal circuit. The refrigerant circulated by the compressor through the auxiliary circuit 18 with the valve 20 open and valve 27 closed passes first into the defrost sections 22 and 23, which correspond to the condenser component of a refrigerating circuit. In these sections, the hot compressed refrigerant condenses and the heat liberated serves to melt the frost accumulated on the evaporator structure 4. The condensed refrigerant then passes quickly through the restrictor 25 and returns to the compressor case 12 as a liquid or as a mixture of liquid and gas producing refrigeration, and rapidly raising the low side pressure and the corresponding input waits to the compressor motor. Thus the defrost circuit comprises in series-flow connection, the compressor unit 1, the defrost section 22 and 23 and restrictor 25. As the defrost circuit is heat exchanged with the accumulator 7, condensation of hot compressed refrigerant takes place in this section to give up its latent heat to the accumulator 7. This causes the liquid refrigerant present in the accumulator to vaporize, at least partially, so that it also returns through the suction line 5 to the compressor case 12 where it increases the low side or case pressure thereby placing a greater load on the motor and causing a further increase in the input watts to the motor. As is more fully described in my aforementioned application, the increased input watts causes the heat output of the motor cooled by the refrigerant to rise rapidly thus providing a large amount of heat for defrosting purposes.

For optimum defrost operation of the system, the restrictor 25 in the auxiliary circuit 18 should be designed to restrict the refrigerant flow in the defrost circuit sufficient to effect condensation of liquid in the defrost sections 22 and 23. Its flow rate for liquid refrigerant will be higher than the flow rate of the capillary restrictor 33 since during defrost operation of the system the low side compressor pressure is higher and therefore the pumping rate in pounds of refrigerant per hour is much higher than during normal refrigeration. Furthermore, it is not desirable to retain any substantial amount of liquid refrigerant in the auxiliary circuit ahead of the restrictor 25 since the retained refrigerant is not available to the compressor case 12 for raising the low side pressure and hence the input watts of the drive motor 10. The refrigerant flowing through the restricting tube 25 and entering the compressor case produces refrigeration in the case. This refrigeration overcomes the heating effect of the increased input watts to the motor and will actually cause the temperature of the entire compressor unit 1 to decrease substantially. All of the heat energy resulting from the increased input watts is removed from the motor compressor by the circulating refrigerant and is made available for defrosting of the evaporator 4. When defrosting is complete, valve 20 is closed and valve 27 opened to return the system to a normal refrigeration on" cycle.

For automatically initiating defrost operation of the system there is employed a suitable electrical control system which periodically energizes a solenoid 29 to open valve 20 and effect initial flow of gaseous refrigerant from the high pressure side of the system through the auxiliary circuit. At the same time condensed refrigerant in the condenser will back flow through valve 27 and the discharge line and into the auxiliary circuit due to the fact that condenser 2 is at a higher pressure than the auxiliary circuit when valve 20 is opened.

An electrical control circuit suitable both for the purpose of initiating and terminating the defrost operation and for controlling the normal operation of the system is illustrated in the drawing. For normal refrigerating control, the circuit comprises a pair of supply lines or conductors 30 and 31 for energizing the compressor motor 10 through a temperature-operated switch 32 in the supply line 30. A temperature sensing device 33 in contact with the evaporator structure 4 operates switch 32 so that during normal operation of the system the compressor motor is energized, for example, whenever the evaporator structure reaches a predetermined maximum temperature of F. and is de-energized when the structure attains a predetermined low temperature of -20 Ff The defrost control portion of the electric circuit comprises a defrost control switch 34 for periodically energizing solenoid 29; the switch 34 and solenoid 29 being connected in series to supply lines 30 and 31 in such a manner that the energization of the solenoid 29 is also under control of the switch 32. The defrost control switch 34 can be any of the known switch means designed to close the circuit to solenoid 29 as a function of time, number of refrigerator cabinet door openings or the like and to break that circuit when the temperature sensed by a temperature sensing element 35 contacting'the evaporator structure 4 is a few degrees above freezing, i.e., such that the evaporator structure has reached a frost-free condition,

In order to obtain the desired operation of the .valve 27,. the solenoid 28 controlling the operation of this normally open valve is connected to the same circuit which controls the operation of the solenoid 29 but in parallel with solenoid 29 so that the closing of the switch 34 also conditions the circuit including solenoid 28 for energization. For the purpose of obtaining the desired time delay action of the solenoid 28 so as to allow the condensed refrigerant in the condenser 2 to back flow into the auxiliary circuit, there is provided an additional temperature responsive switch 50 in the circuit for solenoid 28. This switch 50 which is open during the normal refrigerating cycle and during the initial stages of the defrost period is operated by a sensing device 51 arranged to sense a change in a system condition effected upon or by the opening of the valve 20. In the illustrated embodiment of the invention the sensing device 51 is shown as being in heat exchange relationshipwith that portion of the evaporator structure 4 adjacent the inlet end 52 of the auxiliary circuit 18. During normal operation of the refrigerating system this portion of the evaporator is within the normal temperature ranges for the evaporator, for example between 0 and a -20 F. and the sensing device 51 and switch 50 are designed to maintain switch 50 in an open position at such low temperatures. Upon the opening of valve 20 hot compressed refrigerant from the compressor warms this portion or area of the evaporator structure almost immediately so that within a short interval of time after initial opening of the valve 20, the sensing device 51 in response to this temperature change will cause the switch 50 to close and energize the solenoid 28 thereby closing valve 27. Switch 50 will then remain closed until the sensing device 51 again senses normal refrigerating temperatures even though the circuit to the solenoid 28 may be broken by opening of the switch 34.

It will be understood that the present invention in its broader aspects is not restricted to any particular location of the sensing device 51 on the evaporator struc-. ture 4. In fact, the sensing means for obtaining automatic delayed operation of switch 50 can be arranged at any part of the system which undergoes a change in condition of either temperature or pressure upon the opening of the valve 20. For example, the sensing device 51 could be placed in heat exchange with the suction line between. the point 24 and compressor case since this portion of the suction line, which normally operates in the neighborhood of room temperature during normal refrigeration operation of the system, experiences a substantial temperature drop when it becomes part of the low pressure side of the defrost circuit.

It will be seen that this control circuit is designed to permit energization of the solenoid 29 to open valve 20 and to condition the solenoid circuit for the solenoid 28 for operation only when the switch 32 is also closed to energize the compressor motor 10. Therefore, defrost operation will be initiated only if the compressor is also energized. Once the defrost cycle is initiated, the sensing device 33 will sense only higher evaporator temperatures and switch 32 will therefore remain closed and the compressor will operate continuously during the entire defrost cycle as well as a normal refrigerating cycle immediately following the defrost cycle. The defrost cycle is terminated and the refrigerating cycle initiated by opening of the switch 34 when the sensing device 35 indicates that the evaporator is free of frost. Opening of the switch 34 causes valve 20 to close and valve 27 to open. Switch 32 will open to stop the compressor only when the sensing device 33 again senses the predetermined low evaporator temperature of, for example, 20 F.

By the closing of valve 27 in the normal refrigerating circuit during defrost operation, that portion of the entire system including the condenser 2 and, to a substantial extent the evaporator circuit, are removed from the total effective volume of the system during the defrost cycle with the result that substantially all of the refrigerant charge in the system is available for circulation through the auxiliary circuit for maximum increase of the suction pressure on the compressor 11 and hence the input watts to the motor 10 during both the initial period of defrost operation and also during the latter periods when, in the absence of the valve 27, small, but in some cases significant, amounts of refrigerant would flow through the normal circuit clue to condensation in the condenser 2 resulting from the fact that the head or discharge pressures gradually increase during the defrost cycle as the evaporator becomes warmer. Thus, it will be seen that the present invention combines certain of the advantages of the invention described and claimed in my aforementioned copending application with the advantages derived by the closing of valve 27, with the net result that somewhat higher defrosting temperatures and faster defrosting of the evaporator can be obtained with the present system than with that disclosed in my copending application. The system of the present invention is particularly useful where extreme heat is required for defrost operation as for example when the thermal mass of the evaporator is high and it is desired to bring the entire evaporator structure to defrosting temperatures as quickly as possible.

While there has been shown and described a particular embodiment of the present invention, it is to be understood that the invention is not limited to this particular form and it is intended by the appended claims to cover all modifications within the true spirit and scope of the invention.

What I claim is:

1. A refrigerating system comprising a hermetic compressor unit including a casing and a compressor and a motor for driving said compressor sealed within said casing, a condenser, a fixed flow restrictor, and an evaporator, conduit means connecting said compressor, condenser, fixed flow restrictor, evaporator and casing to form a closed series-flow refrigerating circuit in which said compressor withdraws low pressure refrigerant from said evaporator and through said casing and discharges high pressure refrigerant to said condenser, said motor being cooled by the low pressure refrigerant in said casing, means for periodically warming said evaporator to defrosting temperatures comprising an auxiliary circuit having an inlet end connected to said normal refrigerating circuit between said compressor and said condenser and its outlet end connected to said normal refrigerating circuit between said evaporator and said compressor, said auxiliary circuit including a defrost portion in heat exchange relation with said evaporator and a flow restricting means, conduit means connecting said compressor, said defrost portion, said flow restricting means and said casing to form a series-flow defrosting circuit, a first, normally closed valve in said auxiliary circuit for normally preventing flow of refrigerant through said auxiliary circuit, a second, normally open valve in said normal refrigerating circuit between said compressor and said condenser, and an electrical control circuit for controlling the defrost operation of said system comprising means for opening said first valve to initiate flow of refrigerant from said compressor through said defrost circuit and means responsive to a change in a system coricircuit for closing said second valve.

2. A refrigerating system comprising a hermetic compressor unit including a casing and a compressor and a motor for driving said compressor sealed within said casdition effected by flow of refrigerant through said defrost ing, a condenser, a fixed flow restrictor, and an evaporator,

conduit means connecting said compressor, condenser, fixed flow restrictor, evaporator and casing to form a series-flow refrigerating circuit in which said compressor connected to 'said normal refrigerating circuit between said evaporator and said compressor, said auxiliary circuit including a defrost portion'in heat exchange relation with'said evaporator and restricting means,

conduit means connecting said compressor, said; defrost portion, said flowrestricting means and casing to" form a series-flow. defrosting circuit, 'afrirst, normally closed valve said auxiliary circuitlfor normally preventing flow of refrigerant through .said.auxiliary circuit, a second, "normally open valve in said normal, refrigerating circuit between said compressor andfsaidco'ndenser, and an elec trical control jcircnit ro controlling the defrost operation of said system comprising means for opening said 'firstgva'lve to initiate flow of refrigerant from said compressor'throngh ,saiddefros't circuit and means responsive to' a temperature change adjacent the inlet end of said de- "fr ost portion for; closing said second v ve.

JRefei-enees Cited in .the-iile of this patent I 4 Withdraws low pressure refrigerant from said evaporator AT SQ V v and through :said casing and discharges high pressure re- 12,720,759 Bhilip'p Oct. 18, 19,55

frigerant to said condenser, said motor being cooled by 12,759,339 

